Question Decreasing the Breathing Reflex....Possible?

[Celt]

The Bohr effect describes how binding affinity for O2 to hemoglobin decreases with reduction in pH. This is most beneficial for understanding oxygen unloading in tissue where pCO2 rises and increases the efficiency of oxygen delivery.

What you are talking about is diffusion vs. perfusion limitation. And yes at 1atm both CO2 and O2 are perfusion limited. Meaning the gas exchange across the alveoli occurs more quickly than the blood flows through the length of the capillary associated with the alveoli. if you experience diffusion limitation at 1 atm odds are good you are not diving because if you have a condition that leads to this a physician will not clear you for diving. Given O2 is perfusion limited at a partial pressure of 0.21 atm it is then quite clear that at depth there will be no issue saturating the blood with oxygen. In fact, as we often discuss it is the inverse we concern ourselves with in oxygen management (ie hyperoxia).

However, CO2 is being produced at a constant rate (relatively) and must still be eliminated. But now we’ve changed the dynamics of this substantially and this is seemingly largely related to the densities of the gas. CO2 is elimination is dependent on minute ventilation. That is tidal volume x respiratory rate. At depth with increased gas density the air does not move as freely through the lungs and gas exchange is impaired. The physiology of this does not appear to be fully understood from my reading of the literature. However, suffice it to say we do not eliminate CO2 as efficiently at depth. Further, our basic compensatory mechanism of increased minute ventilation through increased respiratory rate does not appear to work well given the dynamics of gas exchange at depth. The elimination of CO2 as optimized by oxygen displacement at the level of the alveolus is explained by the Haldane effect. But this mechanism seems to be intact at depth.

Thank you, the science is a bit over my head. I don’t know exactly how it works but I done CO2 tolerance training all my life and I’m very relaxed diving. Never experienced any kind of problem with CO2.

 

[Gelirfella]

Most people won’t. But exert yourself at 100m and you might find something different. I’m not sure what CO2 tolerance training is. The cells can accommodate a pretty narrow range of CO2. Anything outside of that starts to cause some issues. I am unaware of anyone being able to train their cellular response to CO2. Apnea training can certainly be done. But most of that has to do with ability to tolerate the hypoxia as far as I understand it. I’m sure CO2 climbs during prolonged breath holds but provided the free diver stays awake when they return to the surface they correct this pretty fast.

 

[Dominik_E]

Gelirfella, well, one regime has been named here already, it is apnea times. But in general, as said many times, I do agree; I also do not expect to see a notable effect in scuba diving air consumption.

 

[Gelirfella]

Why would this be called CO2 training. There’s no mechanism for training CO2 tolerance in the acute setting as far as I know. You can certainly move your set point for CO2. This is seen in people with obstructive airway disease who tolerate very high pCO2 and actually can experience a significantly decreased respiratory drive if their CO2 is dropped to normal levels. But this takes years of chronic exposure. Apnea training is real. But probably more related to improvements in efficient utilization of oxygen than anything related to CO2.

 

[BRT]

Why would this be called CO2 training. There’s no mechanism for training CO2 tolerance in the acute setting as far as I know. You can certainly move your set point for CO2. This is seen in people with obstructive airway disease who tolerate very high pCO2 and actually can experience a significantly decreased respiratory drive if their CO2 is dropped to normal levels. But this takes years of chronic exposure. Apnea training is real. But probably more related to improvements in efficient utilization of oxygen than anything related to CO2.

I'm going to disagree somewhat. No question that I can train myself (and did at one point) to ignore higher levels of CO2. If O2 is not the driver of breathing, and I agree it is not, then training oneself to ignore the need to breathe is in fact CO2 training.

 

[Dominik_E]

Gelirfella, you mean me? Then maybe postings crossed. I was talking about a regime existing where high inspired fO2 moves backward the urge.

 

[Celt]

Most people won’t. But exert yourself at 100m and you might find something different. I’m not sure what CO2 tolerance training is. The cells can accommodate a pretty narrow range of CO2. Anything outside of that starts to cause some issues. I am unaware of anyone being able to train their cellular response to CO2. Apnea training can certainly be done. But most of that has to do with ability to tolerate the hypoxia as far as I understand it. I’m sure CO2 climbs during prolonged breath holds but provided the free diver stays awake when they return to the surface they correct this pretty fast.

It’s the same as altitude training. Basically you’re breathing less than you feel you need to during exercise. What you’re increasing is the time you first feel a need to breathe after a normal exhalation. For instance when brisk walking I’ll breathe normally and then hold an exhalation for 20 steps and then return to normal breathing.

 

[Gelirfella]

I guess it’s training your mind to tolerate the urge to breathe without breathing. But I’d be curious if anyone has ever determined if there is any actual physiologic difference in the respiratory drive as it relates to PCO2 in say an accomplished free diver from the norm. I’m just not sure I’d call it CO2 training. It’s a semantic point though. I agree that CO2 is thing driving you to breathe.

I was talking about a regime existing where high inspired fO2 moves backward the urge.

I’m just saying high inspired O2 does not significantly influence this in vivo. It is tested every day by divers diving with the maximum allowable PO2 who don’t experience this decreased need to breathe because CO2 is more important.

 

[DancinDave]

I remember some experiment from the early 70s in which a lab rat was effectively "drowned" in some aqueous solution saturated with oxygen. Because the dissolved oxygen easily diffused through the aelveolar membranes and into the rat's bloodstream, and the carbon dioxide easily diffused the opposite direction, the rat did not experience the need to breathe in and out. Completely immersed in that 2 liter aqueous/oxygen bath, the rat survived about 3 hours. It died afterwards because it was impossible to remove fluid from the deep lungs.

Can anyone explain why diving with enriched air (or even with pure oxygen) doesn't lessen the breathing reflex? If it were possible to maintain reserve CO2 in the lungs far below normal concentrations, why wouldn't that decrease the reflex?

Don't record-chasing freedivers experience some elimination of that reflex as they hold the torpedo weight and plummet to high pressure depths where oxygen is literally cold-pressed through aelveolar membranes?

I have managed to develop a simple breathing pattern that decreases air usage, extends your dive. Breathe unusually slowly and deeply, both in and out. Only "hold your breath" a couple of seconds max between ending the long-inhale & beginning a slow, long exhale. It takes practice to get good at it but works very well. Obviously, maintaining NEUTRAL buoyancy is a critical item for low air usage. Move leg muscles as little as possible. Fyi. Dave

 

[Dominik_E]

I’m just saying high inspired O2 does not significantly influence this in vivo. It is tested every day by divers diving with the maximum allowable PO2 who don’t experience this decreased need to breathe because CO2 is more important.

Fully agreed. And that is different from static breath holding, where, as Simon Mitchell and others already noted here, basically everyone sees much longer times with O2. Although part of that effect is the hyperventilation part that to some extent also would work with air, O2 adds on that.